|Publication number||US4016230 A|
|Application number||US 05/540,769|
|Publication date||Apr 5, 1977|
|Filing date||Jan 14, 1975|
|Priority date||Apr 29, 1974|
|Publication number||05540769, 540769, US 4016230 A, US 4016230A, US-A-4016230, US4016230 A, US4016230A|
|Original Assignee||Brigend Investments Limited|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (6), Classifications (14)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention relates to the production of a product such as a pallet by a vacuum moulding technique in which a substantially two dimensional array of reinforcement is encapsulated by vacuum forming a thermoplastic sheet around the reinforcement.
It is known to form a pallet by supporting elongate steel reinforcement on pegs fixed to the top of a vacuum forming table, and superimposing a hot sheet of thermoplastic material so that the vacuum draws the hot sheet both around and under the reinforcement. The parts of the hot sheet drawn together under the reinforcement are thus fused together to encapsulate the reinforcement. However, encapsulation of the reinforcement is not complete because the supporting pegs prevent the hot thermoplastic material being drawn underneath the steel reinforcement at the points where the reinforcement is supported. This has the disadvantage that the reinforcement is exposed and may be subject to corrosion under atmospheric conditions, and cavities, previously occupied by the forming table supports, remain in the surface of the moulded product. Dirt may accumulate in the cavities and if, for example, the moulded product is a pallet to be used in an hygenic environment for food handling, the reinforcement corrosion and/or dirty cavities at the load handling surface of the pallet are most undesirable.
In order to overcome this problem, and in accordance
With the present invention, the vacuum forming table is formed in at least two separate sections which are movable relatively to one another in the upright direction perpendicularly to the plane of the table, whereby in use the reinforcement is first supported on a first section or sections which are at a higher level than a second section or sections, vacuum is applied to the second section or sections of the table to draw an overlying sheet of hot thermoplastic material down around the reinforcement above the second section or sections, and when the thermoplastic material is capable of supporting the encapsulated parts of the reinforcement above the second section or sections, the first section or sections are lowered relatively to the second section or sections and vacuum is then applied through the first section or sections to draw the thermoplastic material down around the remainder of the reinforcement above the first section or sections of the table.
The first sections of the table may each comprise a bar extending across the width of the table, the bars being fully retractable into the remainder of the table, whereby in use, the first sections are retracted soon after the vacuum has been created and when sufficient thermoplastic material has filled the gap between the underside of the reinforcement and the top of the forming table for the plastics material to take over the supporting function for the reinforcement. This results in total encapsulation of the reinforcement and enables, for example, the manufacture of a pallet having a smooth deck of plastics material uninterrupted by areas where steel reinforcement is exposed.
Two examples of the use and construction of a vacuum forming table according to the invention will now be described with reference to the accompanying diagrammatic drawings, in which:
FIG. 1 is a vertical section through a vacuum forming table showing a reinforcement resting thereon and a hot sheet of thermoplastic material superposed over the reinforcement;
FIG. 2 is a plan view of the apparatus shown in FIG. 1, along the line II--II in FIG. 1;
FIGS. 3, 4 and 5 are similar views to FIG. 1 showing first, second, and third stages of the process respectively, and,
FIG. 6 and 7 are sections through a second vacuum forming table corresponding to the stages shown in FIGS. 3 and 5.
In FIG. 1 there is shown a vacuum forming table 1 on which rests rectangular-sectioned steel reinforcement 2 which is to be encapsulated by a thermoplastic sheet of material 3 to form a pallet. The vacuum forming table incorporates two elongate bars 4 which are movable relatively to the remainder of the table in a perpendicular direction by means of rods 5 which are raisable by jacks (not shown).
To initiate the encapsulation process the bars 4 are raised as shown in FIG. 3 until the reinforcement elements 2 abut the underneath of the thermoplastics sheet 3. A vacuum is then applied through the vacuum forming tabel 1 to draw the thermoplastic sheet 3 down and around the reinforcement members 2. In order to make forming of the thermoplastic sheet possible it is preheated before being positioned over the reinforcement members on the vacuum forming table. As can be seen in FIG. 3 loops of the hot thermoplastic material are formed below the reinforcement 2 and in order that the thermoplastic material can be formed into a flat surface to form the top of a pallet the bars 4 are lowered to the position shown in FIG. 4 so that the thermoplastics material 3 moulds itself against the planar surface of the remaining sections of the vacuum forming table.
However for a short length of time, the thermoplastics material 3 is unable to support the weight of the reinforcement and so the bars are retained in the position as shown in FIG. 4 until such time as the reinforcement can be at least partially supported by the thermoplastics material. The bars are then withdrawn into recesses 6 so that the tops of the bars lie flush with the remainder of the vacuum forming table surface. The continued application of the vacuum through the vacuum forming table draws the final portions of the thermoplastics material down onto the vacuum forming table surface to complete the encapsulation process. Depending on the time at which the bars are withdrawn so the reinforcement will sink to a greater or lesser extent into the thermoplastic material.
Alternatively as shown in FIGS. 6 and 7 the forming table may be formed in say three sections; two end sections 14 and a central section 15. The end sections 14 are initially raised relatively to the central section 15, on rods 5 raisable by jacks (not shown), to support the opposite edges of the two dimensional reinforcement 2 to cause encapsulation of the central part of the reinforcement. The end sections 14 of the table are then lowered (FIG. 7) so that their upper surfaces are co-planar with that of the central section 15 and vacuum is then applied through the end sections 14 as well to complete the encapsulation of the reinforcement. In this case the end sections of the table will provide the first sections and the central section will provide the second section.
A common source of vacuum may be applied to the sections, the vacuum being applied to the first section or sections when conduits in the first and second sections come into alignment with one another upon lowering of the first section or sections relatively to the second section or sections.
Some means may be necessary to accelerate the cooling and setting of the thermoplastic material which has encapsulated the part of the reinforcement above the second section or sections of the forming table so that the thermoplastic material above the first section or sections of the forming table has not cooled too much before it is subsequently drawn around the parts of the reinforcement above the first section or sections of the forming table Such cooling may be provided by chilling the second section or sections of the forming table or by applying cooling water sprays to the part of the product above the second section or sections of the table after encapsulation of the corresponding part of the reinforcement. Sagging of the thermoplastic material above the first section or sections of the forming table prior to vacuum being applied through this section or sections may be inhibited by applying a positive pressure to the underside of this part of the thermoplastic material, either through the first section or sections of the forming table or otherwise.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US2361348 *||Oct 12, 1939||Oct 24, 1944||Spalding A G & Bros Inc||Process and apparatus for making balls|
|US3238287 *||Apr 27, 1962||Mar 1, 1966||Illinois Tool Works||Method for encapsulating a headed member with a molten material|
|US3875280 *||Oct 17, 1972||Apr 1, 1975||Plasteel Ind Inc||Method for making an integrated reinforced plastic unit|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US4819813 *||Nov 21, 1985||Apr 11, 1989||Lift Verkaufsgerate-Gesellschaft M.B.H.||Device for holding objects and arrangement provided with such devices|
|US5288453 *||Nov 12, 1992||Feb 22, 1994||Custom Pak, Incorporated||Method for forming double walled integral hinge members in blowmolded plastic articles|
|US5407632 *||Oct 8, 1993||Apr 18, 1995||Cadillac Products, Inc.||Twin sheet thermformed structure and method of making same|
|US5813355 *||Oct 21, 1996||Sep 29, 1998||Trienda Corporation||Twin-sheet thermoformed pallet with high stiffness deck|
|US5868455 *||Aug 30, 1996||Feb 9, 1999||Prince Corporation||Vehicle door panel with integral handle and method of manufacture|
|US6174396||Sep 20, 1993||Jan 16, 2001||Davidson Textron, Inc.||Method of manufacturing a trim panel having a handle|
|U.S. Classification||264/510, 264/278, 264/274, 264/554, 425/388, 264/547|
|International Classification||B65D19/00, B29C51/12|
|Cooperative Classification||B65D19/0004, B29C51/12, B65D2519/00562, B65D2519/00432|
|European Classification||B29C51/12, B65D19/00C|